A. Technical Field
The present invention relates to an aqueous coating composition for automotive upholstery, which has excellent coatability to plastic materials, particularly, polyolefin materials.
B. Background Art
As to plastic materials utilized for automotive upholstery, various ones are selected from among such as polypropylene (PP), acrylonitrile-styrene (AS), acrylonitrile-butadiene-styrene (ABS), poly(phenylene oxide) (PPO), poly(vinyl chloride) (PVC), polyurethane (PU) and polycarbonate (PC) in accordance with physical properties demanded to product specifications. In recent years, however, polyolefin materials having excellent recyclability are getting often used in view of environmental protection.
Coatings suitable for upholstery are applied to these plastic materials. However, it is difficult to make the resultant coating films adhere to the polyolefin materials, because the polyolefin materials have low surface activity and are crystalline.
Therefore, a pretreatment to ensure the adhesion, such as plasma treatment and flame treatment, is made. Consequently, the coating process becomes complicated, and this pretreatment is a cause of an increase in costs.
In addition, in order to improve the coatability to the polyolefin, a coating composition is generally allowed to contain a poly(olefin chloride) resin to be a solvent type coating composition in which the poly(olefin chloride) resin is dissolved in an organic solvent. However, when such a solvent type coating composition is stored or handled, not only are there problems of environmental deterioration (such as destruction of ozone layer and occurrence of photochemical smog), but also there are anxieties about occurrence of fires and bad influence upon human bodies, because the solvent easily volatilizes.
Chemical resistance such as engine oil resistance and grease resistance will be demanded to automotive uses.
An object of the present invention is to provide a coating composition for automotive upholstery, with which a 1-coat finish of not yet surface-treated (pretreated) plastic materials such as polyolefin materials can be performed, and which is aqueous, and excellent also in chemical resistance.
The present inventors made various experiments to solve the above-mentioned problems. As a result, they completed the present invention by verifying that, if an emulsion type is used as the poly(olefin chloride) resin, and if the chlorination degree thereof is adjusted to a specific ratio, and if this poly(olefin chloride) resin is combined with a large amount of emulsion of a pure acrylic resin within the specific ratio range, then the use of the organic solvent can be omitted or diminished, and further, the 1-coat finish of the plastic materials such as polyolefin materials can be performed, and the chemical resistance can also be enhanced.
That is to say, an aqueous coating composition for automotive upholstery, according to the present invention, comprises a resin emulsion as an essential component, wherein the resin emulsion includes poly(olefin chloride) resin emulsion A and pure acrylic resin emulsion B in a weight ratio (A/B) of 25/75xcx9c30/70 in terms of solid content, wherein poly(olefin chloride) resin emulsion A is an emulsion of a poly(olefin chloride) resin having a chlorine content of 22xcx9c25 wt % in terms of solid content and a weight-average molecular weight of 60,000xcx9c80,000, and wherein pure acrylic resin emulsion B is an emulsion of a pure acrylic resin having a glass transition temperature of not lower than 40xc2x0 C.
When the above aqueous coating composition for automotive upholstery, according to the present invention, is a lacquer paint, it is preferable that the composition further comprises a scaly inorganic powder in a ratio of 60xcx9c75 parts by weight per 100 parts by weight of the resin emulsion in terms of solid content.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.
(Aqueous Coating Composition)
The aqueous coating composition for automotive upholstery, according to the present invention, comprises a resin emulsion as an essential component, wherein the resin emulsion includes poly(olefin chloride) resin emulsion A and pure acrylic resin emulsion B. The total ratio of these two kinds of resin emulsions is preferably in the range of 15xcx9c30 wt %, in terms of solid content, of the entirety of the coating composition.
In the present invention, usually, the poly(olefin chloride) resin and the pure acrylic resin are emulsified separately from each other, and then mixed together.
As to the above resin emulsion, the poly(olefin chloride) resin or pure acrylic resin is particulately dispersed in an aqueous medium, and the particle surfaces thereof are stabilized with such as emulsifiers, surfactants, or dispersants.
(Poly(olefin chloride) resin)
The poly(olefin chloride) resin gives the coating composition sufficient coatability to polyolefin materials, because the polyolefin has affinity for plastic materials to be coated therewith, particularly, polyolefin materials, and further because the polyolefin is polarized by chlorination to enhance its film formability.
Examples of the polyolefin include: homopolymers of such as ethylene and propylene; random copolymers or block copolymers obtained by copolymerizing two or more monomers such as olefin monomers (e.g. ethylene, propylene, 1-butene, 1-pentene, 1-heptene and 1-octene) and vinyl monomers having a terminal vinyl group (e.g. vinyl alkyl ethers, vinyl chloride and vinyl acetate); hydrogenated products from copolymers of such as styrene, butadiene, isoprene and dicyclopentadiene. These may be used either alone respectively or in combinations with each other. Although not especially limited, polypropylene is preferable because it is easily available and has high adhesion.
It is necessary that the poly(olefin chloride) has a weight-average molecular weight in the range of 60,000xcx9c80,000. In the case where the weight-average molecular weight is less than the above range, swelling with engine oil easily occurs, therefore the engine oil resistance is low. In the case where the weight-average molecular weight is more than the above range, the viscosity becomes high in the emulsifying step, therefore the emulsification is difficult, and further, the storage stability is also bad.
It is necessary that the poly(olefin chloride) has a chlorine content of 22xcx9c25 wt % in terms of solid content. In the case where the chlorine content is less than the above range, the affinity and the compatibility between the poly(olefin chloride) and the pure acrylic resin are both so poor that it is difficult to obtain a uniform coating film. On the other hand, in the case where the chlorine content is more than the above range, the adhesion to polyolefin materials is inferior.
In the present invention, the poly(olefin chloride) may be modified (grafted) with an unsaturated polycarboxylic acid and/or an acid anhydride thereof, because the compatibility between the poly(olefin chloride) and the pure acrylic resin is thereby improved to enhance the water dispersibility. If the poly(olefin chloride) is modified with the acid anhydride and/or carboxylic acid, then the acid anhydride group and/or carboxyl group thereof is in the form of a free radical and/or reacts with a basic substance to form a carboxylate anion, with the result that the water solubility is displayed. Therefore, the modified poly(olefin chloride) is easily emulsified and has high water dispersibility. As a result, the storage stability of the aqueous coating composition is enhanced.
Examples of the unsaturated acid anhydride and/or carboxylic acid include maleic acid, fumaric acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid and itaconic anhydride. These may be used either alone respectively or in combinations with each other. Although not especially limited, maleic acid and maleic anhydride are preferable because they are easily available.
(Pure acrylic resin)
Because the above poly(olefin chloride) has a low level of coating film strength and weather resistance, the pure acrylic resin used in the present invention is a component to make up for this and to give the present invention aqueous coating composition the engine oil resistance, the contamination resistance, and the solvent resistance along with the coating film strength and the weather resistance.
The pure acrylic resin is a resin obtained by homopolymerizing or copolymerizing acrylic monomers such as (meth)acrylic acid, (meth)acrylic monomers containing a hydroxyl group, (meth)acrylic acid esters and (meth)acrylonitrile. In short, the pure acrylic resin is a styrene-free acrylic resin. The reason therefor is that styrene deteriorates the engine oil resistance because the solvent resistance of styrene is inferior.
Specifically, the pure acrylic resin is obtained by homopolymerizing or copolymerizing acrylic monomers containing a hydroxyl group, a carboxyl group, or an ester group. Examples of the acrylic monomer containing a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and xcex5-caprolactone adducts thereof. Examples of the acrylic monomer containing a carboxyl group include (meth)acrylic acid. Examples of the acrylic monomer containing an ester group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and lauryl (meth)acrylate.
It is necessary that the pure acrylic resin has a glass transition temperature (Tg) of not lower than 40xc2x0 C. In the case where the glass transition temperature of the pure acrylic resin is lower than 40xc2x0 C., coating film hardness sufficient for automotive upholstery is not obtained, therefore the scratch resistance is not satisfactory. Hereupon, the glass transition temperature is a value determined by the plastic transition temperature measurement method according to JIS-K-7121.
(Emulsification)
The poly(olefin chloride) resin or pure acrylic resin has so high hydrophobicity as to be difficult to stably disperse into water. Thus, the poly(olefin chloride) resin is emulsified with an emulsifier or basic substance.
The combining ratio of the emulsifier is fitly set in accordance with the combining ratio of the poly(olefin chloride) resin, the pure acrylic resin, the basic substance, or water, but, for example, in the case of the poly(olefin chloride) resin, the combining ratio of the emulsifier is preferably in the range of 3xcx9c40 parts by weight, more preferably 10xcx9c25 parts by weight, per 100 parts by weight of the resin. In the case where the ratio of the emulsifier is less than 3 parts by weight, the storage stability of the emulsion is low, and further, the aggregation or precipitation easily occurs on the way of polymerization in the below-mentioned production process for the emulsion. On the other hand, in the case where the ratio of the emulsifier is more than 40 parts by weight, a large amount of emulsifier remains in the coating film, with the result that the water resistance or weather resistance of the coating film is deteriorated.
The emulsifier is not especially limited, but examples thereof include: nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenol ethers, polyoxyethylene aliphatic esters, polyoxyethylene polyhydric alcohol fatty acid esters, polyhydric alcohol fatty acid esters, polyoxyethylene propylene polyols, and alkylolamides; anionic emulsifiers such as alkylsulfate ester salts, alkylphenolsulfonic acid salts, and sulfosuccinic acid esters; amphoteric emulsifiers such as alkylbetaines and alkylimidazolines; resin type emulsifiers such as polyoxyethylene-group-containing urethane resins and carboxylate-salt-group-containing urethane resins; and cationic emulsifiers such as imidazoline laurate, lauryltrimethylammonium chloride, stearylbetaine, and distearyldimethylammonium chloride. These may be used either alone respectively or in combinations with each other. Among these, the nonionic emulsifiers are preferable, because they have no ionic polar group of high hydrophilicity and therefore make the water resistance of the coating film good.
As to the emulsifier, reactive emulsifiers are also usable besides the above-mentioned non-reactive emulsifiers. The joint use of the reactive emulsifier with the non-reactive emulsifier enhances the water resistance of the coating film. The reactive emulsifier, for example, contains a reactive group, such as radical-polymerizable unsaturated bond, as well as a hydrophilic group (e.g. polyethylene oxide group, hydroxyl group, carboxyl group, sulfonic acid group, sulfuric acid group, amino group) and a hydrophobic group (e.g. alkyl group, phenyl group, fluoroalkyl group, polysiloxane group). Examples of the reactive emulsifier include: Adeka Reasoap NE-10, NE-20, NE-30 having an allyl ether group, a polyethylene oxide group and a nonylphenyl group (made by Asahi Denka Kogyo K.K.); SE-10N having an allyl ether group, a polyethylene oxide group, a sulfuric acid group and a nonylphenyl group (made by Asahi Denka Kogyo K.K.); NOIGEN RN-20, RN-30, RN-50 having a propenyl group on a phenyl group in a polyoxyethylene nonyl phenyl ether group (made by Dai-ichi Kogyo Seiyaku Co., Ltd.); HS-10, HS-20 having a propenyl group on a phenyl group in a polyoxyethylene nonyl phenyl ether sulfate ester group (made by Dai-ichi Kogyo Seiyaku Co., Ltd.); S-120A, S-180A having an allyl group and a sulfonic acid group (made by Kao Corporation); and compounds having a methacryloyl group or acryloyl group (made by NIPPON NYUKAZAI Co., Ltd.), such as Antox MS-60 (=bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfate ester salt), RMA-564, RMA-568, RMA-506 (=polyoxyethylene nonyl phenyl ether acrylates), RMA-1120, MPG130-MA (=polyoxyethylene alkyl ether methacrylates), and MA-30, MA-50, MA-100 (=polyoxyethylene methacrylate esters). These may be used either alone respectively or in combinations with each other. Among these, the reactive emulsifiers having a methacryloyl group or acryloyl group are preferable because they are easily copolymerizable with acrylic monomers in the below-mentioned production process for the emulsion composition.
The combining ratio of the basic substance, used as a neutralizer, is also adjusted in accordance with the combining ratio of the poly(olefin chloride) resin, the pure acrylic resin, the emulsifier, or water. Particularly, the combining ratio of the basic substance is determined in consideration of sufficiently neutralizing an acidic functional group in such as poly(olefin chloride) resin or emulsifier, but is, for example, in the range of 0.1xcx9c5 weight % of the entirety of the emulsion. The pH of the emulsion, determined by combining the basic substance, is preferably in the range of 7xcx9c11, more preferably 7.5xcx9c10.5, most preferably 8xcx9c10. In the case where the pH of the emulsion is less than 7, the neutralization is not sufficient, therefore the storage stability of the emulsion might be low. On the other hand, in the case where the pH of the emulsion is more than 11, an excess of free basic substance exists in the emulsion, therefore the emulsion has so strong a smell of amine as to be difficult to use.
The basic substance, used in the present invention, adds to the acid anhydride group and/or carboxyl group of the poly(olefin chloride) resin, and/or neutralizes these groups, thereby serving to enhance the hydrophilicity of the modified poly(olefin chloride) and, as a result, to improve the storage stability of the emulsion.
The basic substance is not especially limited, but examples thereof include at least one of an amine compound and ammonia. Examples of the amine compound include: monoamines such as trimethylamine, triethylamine, butylamine, dibutylamine and N-methylmorpholine; polyamines such as ethylenediamine, hexamethylenediamine, piperazine, isophoronediamine, triethylenediamine and diethylenetriamine; and alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine and 2-amino-2-methylpropanol. These may be used either alone respectively or in combinations with each other. These may be jointly used with ammonia.
The combining ratio of water is preferably in the range of 50xcx9c95 weight %, more preferably 60xcx9c85 weight %, most preferably 65xcx9c80 weight %, of the entirety of the emulsion. In the case where the combining ratio of water is less than 50 weight %, the nonvolatile solid content in the emulsion is too much, therefore the storage stability of the emulsion might be deteriorated due to easy occurrence of such as aggregation. On the other hand, in the case where the combining ratio of water is more than 95 weight %, the workability is bad in the below-mentioned production process for the emulsion, and further, when the emulsion is for example used for a coating such as aqueous primer coating composition or for ink, the amount of the poly(olefin chloride) resin which is a main component is relatively small, therefore no sufficient performance is obtained.
The average particle diameter of polymer particles including a major proportion of poly(olefin chloride) resin or pure acrylic resin in the emulsion is not especially limited, but is preferably in the range of 0.01xcx9c10 xcexcm, more preferably 0.03xcx9c5 xcexcm, most preferably 0.05xcx9c1 xcexcm. In the case where the average particle diameter of the polymer particles is smaller than 0.01 xcexcm, a large quantity of emulsifier is necessary, therefore the water resistance and the weather resistance of the coating film are deteriorated. On the other hand, in the case where the average particle diameter of the polymer particles is larger than 10 xcexcm, the storage stability of the emulsion is deteriorated, and further, the volume of the polymer particles is too large, therefore much melting heat and time to form a coating film is necessary, and the heat flowability is deteriorated, and, when for example used for a coating such as aqueous primer coating composition, the properties of the coating film such as appearance, water resistance and solvent resistance might be deteriorated. (Combining ratio between emulsions A and B):
The combining ratio (A/B) between poly(olefin chloride) resin emulsion A and pure acrylic resin emulsion B is in the range of 25/75xcx9c30/70 in terms of solid content by weight. In the case where this combining ratio (A/B) is less than 25/75, the amount of the poly(olefin chloride) is too small, therefore the adhesion to materials is insufficient. In the case where this combining ratio (A/B) is more than 30/70, the amount of the pure acrylic resin is too small, therefore the chemical resistance such as engine oil resistance is insufficient.
(Lacquer Paint)
When the coating composition according to the present invention is a lacquer paint, this composition usually further comprises a scaly inorganic powder such as talc, mica, or aluminum flake. The combining ratio of the scaly inorganic powder is preferably in the range of 60xcx9c75 parts by weight per 100 parts by weight of the resin emulsion in terms of solid content. In the case where the combining ratio of the scaly inorganic powder is less than 60 parts by weight, contaminators easily intrude, with the result that the chemical resistance such as engine oil resistance tends to be deteriorated. In the case where the combining ratio of the scaly inorganic powder is more than 75 parts by weight, the alkali resistance tends to be deteriorated.
(Other Components)
As to the present invention aqueous coating composition for automotive upholstery, the above essential resin emulsion can fitly be combined with other aqueous resins, if necessary. Water-soluble acrylic resins are the most preferable of the above other aqueous resins, but emulsions of resins other than the water-soluble acrylic resins, such as polyester resin emulsions, polyurethane resin emulsions, epoxy resin emulsions, or amino resin emulsions, may also be combined.
The aqueous coating composition for automotive upholstery, according to the present invention, can further comprise other components which are usually added to coatings, if necessary. Examples thereof include: additives such as surfactants, neutralizers, stabilizers, thickeners, defoamers, surface conditioners, ultraviolet absorbents, and antioxidants; inorganic fillers such as silica; conductive fillers such as conductive carbon, conductive fillers, and metal powders; and auxiliary components such as organic reformers, plasticizers, and additives.
Examples of colorants, which may be mixed into the present invention aqueous coating composition for automotive upholstery, include: inorganic pigments such as titanium oxide, carbon black, iron oxide, chromium oxide, and Prussian blue; organic pigments such as azo pigments, anthracene pigments, perylene pigments, quinacridone pigments, indigo pigments, and phthalocyanine pigments; and dyes.
The aqueous coating composition for automotive upholstery, according to the present invention, can further comprise an organic solvent if the ratio thereof is not more than 20 weight % of water in the resin emulsion. The inclusion of the organic solvent improves the workability and enhances the dispersibility of such as pigments. However, generally, the absence of the organic solvent has more advantage of enhancing the storage stability of the emulsion and fitting with recent restrictions on organic solvents. Examples of such an organic solvent include: aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane and octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane and cyclopentane; esters such as ethyl acetate, n-butyl acetate, isobutyl acetate and amyl acetate; ethers such as n-butyl ether and isobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, isopropanol, n-butanol, 2-butanol, n-propylene glycol and isopropylene glycol; cellosolves such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether and ethylene glycol monoethyl ether acetate; carbitols such as diethylene glycol monoethyl ether; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether and propylene glycol monobutyl ether; and other solvents such as dioxane, N-methylpyrrolidone, dimethylformamide and diacetone alcohol.
(Objective Materials)
The plastic material, which is an object to which the present invention aqueous coating composition for automotive upholstery is coated, is not especially limited, but examples thereof include: polyolefins such as polypropylene (PP) and polyethylene (PE); acrylonitrile-styrene (AS), acrylonitrile-butadiene-styrene (ABS), poly(phenylene oxide) (PPO), poly(vinyl chloride) (PVC), polyurethane (PU) and polycarbonate (PC).
(Coating method)
The method for coating the present invention aqueous coating composition onto the plastic material may be performed either by air spray coating or airless spray coating.
The aqueous coating composition is, for example, coated such that the dried-film thickness will be preferably in the range of 10xcx9c50 xcexcm, more preferably 15xcx9c25 xcexcm. In the case where the dried-film thickness is less than 10 xcexcm, the thickness might be too thin to obtain a uniform film. On the other hand, in the case where the dried-film thickness is more than 50 xcexcm, there tends to occur problems of such as coating film cracking.
The step of drying the coating film may be carried out at room temperature, but is preferably carried out by heating in the range of 60xcx9c80xc2x0 C. to improve the workability or physical properties.
(Effects and Advantages of the Invention)
The aqueous coating composition for automotive upholstery, according to the present invention, enables a 1-coat finish of not yet surface-treated (pretreated) plastic materials, such as polyolefin materials, to be performed with this aqueous coating composition, and, because of being aqueous, involves none of the environmental deterioration, the occurrence of fires, and the bad influence upon human bodies, and further, is excellent also in chemical resistance, such as engine oil resistance and grease resistance, and is fit for such as lacquer paint.